The thrust of our research effort has been to identify molecules of the human cell surface, to determine the chromosomal location of the genes encoding these molecules, to biochemically characterize these molecules and to analyze their function. We have used immunological techniques (antibody and cytotoxic T cells) to define embryonic, tissue-specific and tumor-specific cell surface molecules which appear to mediate the interaction of specific cells with other cells, with each other or with the extracellular milieu. We have prepared antibody probes which have allowed us to define and investigate a molecule, encoded by a gene on a portion of human chromosome 7, which is the receptor for the polypeptide hormone epidermal growth factor. Binding of this hormone to its receptor causes the cell to proliferate. We are seeking to define the complex series of events which this simple hormone-receptor interaction triggers, culminating in the division of the cell. Until recently, no cell culture systems existed to investigate the relationship of hepatitis B virus (HBV) and hepatocellular carcinoma. Using a cell line which we derived from a patient with hepatocellular carcinoma which contains HBV integrated at a single unique site, we are attempting to find if the site of HBV integration plays a role in the induction of cell proliferation and the development of liver parenchymal cell tumors.